How do investment banks (IBs) span informational boundaries and influence mergers and acquisitions (M&As)? By linking boundary-spanning with a network embeddedness perspective, we redefine the boundaries of focal firms and the roles of IBs. In particular, in the process of acquisition, firms build intra-firm ties by hiring IBs and relying on their inter-firm networks. We argue that IBs perform both an information-obtaining and an information-disseminating role across internal and external boundaries. IBs' informational boundary-spanning roles become especially salient when targeting private firms. By analysing 1776 M&A deals with a series of interviews in China, we provide support for our predictions and suggest that IBs are rainmakers rather than supportive agents.